A cooling system for cooling a laser medium of a solid-state laser device and an excitation lamp for applying excitation light to the laser medium in the prior art comprising, as shown in FIG. 10, a laser medium 10 accommodated in a transparent first cooling pipe 12, and an excitation lamp 11 is accommodated in a transparent second cooling pipe 13. Said two cooling pipes are communicated with each other through a communication pipe 17 for circulating a cooling water to the cooling pipes and the communication pipe.
However, the above-mentioned solid-state laser device comprises each laser medium and each excitation lamp accommodated in the respective cooling pipes through which the communication pipe is communicated and into which the cooling water is feeded by the pump, and a flow passage in each cooling pipe is narrow, and there are present any projections in the flow passage, so that a pressure loss of the cooling water becomes large. As a result, a flow rate of the cooling water in each cooling pipe is reduced, and accordingly it is difficult to obtain a sufficient cooling effect in each cooling pipe. Thus, a limited electric power to be applied to the excitation lamp is suppressed to reduce a laser power from the laser medium.
If a large electric power greater than the limited electric power is applied to the excitation lamp, there is a possibility that the laser medium will be broken.
Generally, the solid state laser device provided with the laser medium and the excitation lamp for applying excitation light thereto, as mentioned above, prevents heat accumulation in the laser medium and the excitation lamp due to optical pumping by accommodating the laser medium in the transparent first cooling pipe and accommodating the excitation lamp in the transparent second cooling pipe to thereby cool the laser medium and the excitation lamp with the cooling water.
If the laser medium is heated, a laser beam will be expanded by a thermal lens effect to cause a reduction in laser power. If the laser medium is further heated, there is a possibility that the laser medium will be broken.
In Japanese Utility Model Laid-open Publication No. 57-175452, there is disclosed a technique such that an adverse wavelength light-absorbing material is sealed in a space of a double pipe surrounding a laser rod. However, this technique has a possibility of aged deterioration of the adverse light-absorbing material.
In Japanese Utility Model Laid-open Publication No. 58-11268, there is disclosed a solid-state laser oscillation device, wherein as laser rod side and an excitation lamp side are partitioned each other, having a laser head formed with two water passages for individually cooling the laser rod and the excitation lamp, and a pair of pure water circulating units individually connected to the two water passages. Each pure water circulating unit includes a water temperature control device and a water tank. A water temperature of a pure water to be circulated in the water passage for the laser rod is maintained at a temperature higher than ordinary temperature, which water temperature is higher than a water temperature of a pure water to be circulated in the water passage for the excitation lamp. Thus, the water tanks must be individually provided in the pure water circulating units.